| The research on greenhouse gases such as CO2 has become a hot spot in the context of global environmental change and climate warming.For a long time,fossil fuels as the main energy has been widely used,being considered to be an important source of increasing greenhouse gases.Hydro-power had got a promotion as clean energy,while in recent years,there has come a wide controversy aroused by the greenhouse gas issue about hydro-power.The most attracted in the word among the numerous reservoirs of China is the Three Gorges reservoir,and the study on the ecological environment of the reservoir area,including greenhouse gases,has been the focus of research among global scholars.Hence,making the various sources and contributions of atmosphere CO2 in the the reservoir and rivers clear is very important.This study had selected a tributary bay-Zhuyi River of the Three Gorges Reservoir as the research object,and the work stared from April 2016 to March 2017,during which the stratified sampling was discontinuous,and typical months had been selected in seasons.Works contained the measurement of hydrochemical parameters(nitrogen,phosphorus,silicon,dissolved organic carbon,water temperature,pH,alkalinity,CO2 flux,etc.),analysis of carbonate balance and spatial and temporal distribution of CO2 in river,and exploring main factors affecting the change of inorganic carbon,to further analyze the results of Three Gorges Reservoir on the carbon exchange process occurring in the interface between water and air in reservoir tributary.The results are that:(1)The nutrient concentrations had the seasonal variation under the impact of water mass exchange between trunk stream and tributary and basin pollution status.The maximum and minimum nitrogen concentration occurred in spring and autumn respectively,and the same with phosphorus.The contents of nitrogen and silicon nutrients were always at a high level,and the total nitrogen and nitrate nitrogen content were higher than the average level of the world.(2)The carbonate equilibrium change was following behind the CO2 change in Zhuyi river.The balance moved to the left during the "sink" period,and the maximum offset of bicarbonate ion reached to 6.25mmol/L.On the contrary,the balance moved to right during "source" period.Besides,the rainfall in basin also had effect on the carbonate equilibrium in river,especially,the ammonia pollution from basin following the runoff caused by rainfall into river had an obvious influence on H+,which could affect the equilibrium direction.(3)The CO2 in Zhuyi River were mainly from water biological aerobic respiration,sediment release and groundwater recharge in low water condition.The dissolved inorganic carbon consumption was mainly by algae photosynthesis.The change of the partial pressure of CO2(p(CO2))were totally different between estuary and upstream in Zhuyi river.Firstly,estuary was the CO2"source" area all the year around,and the lowest p(CO2)was 31.0Pa,the highest is 185.5Pa respectively,and the average monthly CO2 flux was estimated to be 0.269?2.216mmol/(m2 · h).Secondly,there were some water temperature stratification in 0-5m in upstream in spring and summer,which could retard the release of CO2 from the deeper water and sediment to the air.Plus,the surface of algae photosynthesis were intense in these two seasons,so the upstream was the CO2"sink" area in spring and summer,and the p(CO2)was 5.14?39.26Pa in surface water,and was 31.94?268.65Pa in deep water respectively.While,there was no temperature stratification and the water temperature decreased in winter,thus the release of CO2 from sediment to the air was accelerated,and the whole river was the CO2 "source" area,and thep(CO2)in river was 35.36?231.42P.The carbon exchange flux occurring in the interface between water and air was lower in the year-round,and the monthly average exchange flux was about 0.058mmol/(m2 · h),which was far below the world average flux of rivers and lakes.Compared to the natural river,Zhuyi River was a weak CO2 "source" area. |
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